Saving or building, which is more sensible?

But with older people, where the man is the main earner, it is often the case that the man, meaning me, hardly cares about the money. Since we got married, she takes out money, hands in the transfer receipts, we don’t do online banking, only with slips, I get my allowance so I have some money on me, we both have a card. I don’t think she ever felt it wasn’t her money. At least I hope so. Karsten

Sure, theoretically it doesn't matter after the tax return. Still, there are unfortunately many men who theoretically say "it's OUR money" but often in concrete situations say that they now want XY and, after all, bring most of the money home and therefore should decide. This doesn’t even have to be said out loud but is often implied. And I think that this is not even malicious or conscious.. but it still conveys to the woman a correspondingly low appreciation of her work (whether with children at home or at a job). In the tax refund, it is also not so easy to see how much SHE has contributed to the total amount. But I think the problem will decrease as the generations come along in which it is more common in (all of) Germany that both work.

Simply both into the IV and no one will be disadvantaged

the tax class doesn't matter. NO ONE is ever disadvantaged. If you don't understand that -> tutoring with the tax advisor!